Wet Hardwood Floor Cupping

The simplest way to think of wood floor cupping is to imagine the edges of each plank sticking up higher than the centers.

Wet hardwood floor cupping.

Wood is hygroscopic in nature and thereby tends to absorb moisture from its surroundings causing problems in hardwood floors. Cupping in solid wood floors cupping occurs in solid wood flooring as a result of an elevated mc in the bottom of the flooring compared with the mc of the face. Underlayment and or subfloor that is too wet at the time of installation will cause wood floor cupping. As you can see moisture and wood don t go well together.

When the moisture increases the wood swells and then when it decreases the wood shrinks. This expansion can be in the form of cupping the center of the board is lower than the edges or crowning the center of the board is higher than the edges. If you imagine a picture of a child drawing a boat in the water then the water will give you a good idea of what a cupped floor looks like. It ends up looking a little like an accordion.

The general effect is easy to demonstrate by putting a small strip of paper onto a small drop of water. A cupped floor develops as moisture from the underlayment or subfloor moves upward through the hardwood as the back of the wood becomes wetter than the face of the wood.